The present invention relates to new and improved stable disposable absorbent structures and more particularly, to diapers and sanitary napkins containing the new absorbent structures as the absorbent core of the product.
Disposable absorbent products have been known for some time including such products as disposable diapers, sanitary napkins, wound dressings, bandages, incontinent pads and the like. These products incorporate an absorbent batt which is used to absorb and hold or contain body fluids. Initially in many of these products, especially diapers and sanitary napkins, the absorbent batt comprised what is termed "wadding" or plies of tissue. The wadding was disposed between a liquid-impermeable backing and a liquid-permeable facing and the plies of tissue were used to absorb and hopefully contain the liquid within the product. A diaper which utilizes such an absorbent batt is disclosed in U.S. Pat. No. Re. 26,151.
The wadding type of product was replaced for the most part by an improved absorbent batt which comprises what is termed "fluffed wood pulp fibers". This absorbent batt comprises a layer of individualized wood pulp fibers with the layer having substantial thickness. A diaper which incorporates such a fluffed wood pulp absorbent batt is described in U.S. Pat. No. 2,788,003. This diaper had improved absorbent capacity and somewhat better containment ment than a diaper using a wadding layer. Also the fluffed wood pulp layer is quite soft, flexible and conformable and, hence, produces an improved diaper over diapers using wadding as the absorbent layer.
Though the fluffed wood pulp absorbent batts have improved capacity, the efficiency with which the capacity is used in a diaper or sanitary napkin is poor. One of the reasons for this is that the fluffed wood pulp absorbent batt tends to break apart upon flexing. Furthermore, once the absorbent batt has accepted a substantial amount of liquid, the cellulosic fibers tend to collapse, sometimes causing liquid to be squeezed from the product and to leak. Another reason is that the fluid to be absorbed is generally deposited in a localized area within the absorbent batt and the ability of the fluid to move along the plane of the batt is poor. The fluid tends to follow a radial wicking path and, consequently, moves to the closest edge of the batt where it generally is no longer contained and the product leaks. The only way in which the capacity can be increased is to add more pulp thus compounding the problems already present and thickening the product making it more bulky.
In answer to some of the problems, U.S. Pat. No. 3,017,304 incorporated in the absorbent batt a densified paper-like layer. This paper-like layer acts as a wick i.e., liquid which is placed on the layer tends to move rapidly along the plane of the layer. When incorporated in combination with fluffed wood pulp fiber, the resultant product uses the absorbent capacity of the fluffed wood pulp much more efficiently. However, the paper-like densified layer is subject to fracture and though it stabilizes the absorbent batt to some degree, fracturing occurs too frequently. Diapers which incorporate this paper-like layer combined with fluffed wood pulp are disclosed and described in U.S. Pat. Nos. 3,612,055 and 3,938,522. This concept of combining wicking ability or a capillary skin layer with fluffed wood pulp fibers has gained wide acceptance in many absorbent products, including disposable diapers and sanitary napkins. Even though these products make much greater use of the capacity of the absorbent batt, they still do not totally contain the absorbed liquid. It is probable that these products will leak before the full capacity of the batt is used for the absorption or, at the very least, before the entire liquid void by the user is absorbed. This is especially true when pressure is placed on the batt while wet. For example, a baby sitting down on a previously wetted diaper will very often cause the batt to leak.
A number of years ago in answer to increasing capacity of absorbent products "superabsorbent materials" i.e., materials which will absorb many times their weight of liquid, were developed. Since the development of such materials, attempts to incorporate them in absorbent products, such as diapers, to enhance the absorption performance of these products have been made. Theoretically, a minimum amount of superabsorbent incorporated in a product would make that product perform as well or better than the prior art products. Perhaps one of the first products to incorporate such a superabsorbent material in a disposable diaper is disclosed in U.S. Pat. No. 3,670,731. This patent discloses an absorbent dressing comprising an absorbent layer sandwiched between a permeable facing and an impermeable backing sheet. The absorbent layer contains water-insoluble cross-linked hydrocolloid polymer as the superabsorbent material.
Even though superabsorbent materials have been available for some time, they have not gained wide acceptance in absorbent products such as disposable diapers, sanitary napkins, incontinent pads and the like. A primary reason for this lack of acceptance of superabsorbents is failure to develop a product capable of economically utilizing the highly increased absorptive capacity of the superabsorbent material. In order to economically utilize a superabsorbent, the liquid being absorbed must be readily accepted and placed in contact with the superabsorbent material. Furthermore, as the superabsorbent material absorbs liquid it must be allowed to swell. If the superabsorbent is prevented from swelling, it will cease absorbing liquid. Hence, if the superabsorbent material is to function in absorbent products such as diapers, sanitary napkins and incontinent pads, wherein the liquid to be absorbed is placed in a small void area, the structure of the absorbent layer containing superabsorbent materials must have certain characteristics. Over the years a number of techniques have been disclosed in an attempt to provide structures which make efficient use of the superabsorbent material. Such products are disclosed in U.S. Pat. Nos. 4,103,062, 4,102,340 and 4,235,237. In addition, methods for incorporating superabsorbents into suitable layers or suitable configurations which can be placed in an absorbent product are disclosed in U.S. Pat. Nos. 4,186,165, 4,340,057 and 4,364,992. To date, none of these products has met with any substantial commercial success.
The present invention provides a new and improved absorbent product which is dimensionally stable when in use and which possesses an absorbent core containing superabsorbent material, cellulosic fibers and resillent fibers. The new absorbent product will contain absorbed liquid even when pressure is placed upon the product during use.